The present invention relates to lumber grading, and more particularly to a lumber grading system for providing a lumber cutting solution for a piece of lumber, as needed for example by a classification and trimming computer unit operating a saw machine in a sawmill.
The grading station is the cornerstone of any sawmill. It is at this station that the lumber is evaluated usually by human graders. The judgment of a grader is capital since he is responsible of attributing a grade to the piece of lumber and routing the piece according to the grade for proper classification and preparation. Once the grader has examined the piece, a mechanical conveyor system directs the piece accordingly in the production line. The decision of the grader is very important since it determines the treatment to be carried out on the piece. Cutting operations will then be performed to transform the piece of lumber into a finished product ready for distribution. The optimization of the sawmill is thus left to human judgment. If the grader judges too favourably the pieces of lumber, the customers will not receive the expected products at the quality level. Conversely, if the pieces are judged too strictly by the grader, the sawmill will sell products of good quality under the seal of second quality at lesser costs. There is thus a dilemma at this level. Each person though having the same training may have a different appreciation for a same piece of lumber. The sawmill thus largely depends on grading station since all the produced pieces must be subjected to a visual inspection. The current rate is about 50 to 60 pieces per minute per grading station. This requires intense concentration to analyse and judge one piece per second. A sawmill having only one grading station can produce no more than 60 pieces per minute. To increase production, one or two additional grading stations must be implemented. Though it seems easy to add additional grading stations, reality is quite different. In most of the sawmills, the physical space is very limited and outstanding ingenuity must be exercised to achieve such a change. Even when the physical space is appropriate, the addition of another conventional system involves high costs at the mechanical level.
The policy in the presently operating sawmills is often as follows. If the grader has a doubt on the quality of a piece, he/she must downgrade it. This causes a diminution of the value-added of the products. Maintenance costs of the complex mechanical systems and the production time losses related to the grading stations represent important costs.
Known in the art is U.S. Pat. No. 6,031,567 (Johnson) which discloses a method and an apparatus for video lumber grading, so that the human graders can work at a remote location from the lumber conveyors, in a better environment for concentration. The apparatus captures video images of lumber and displays the images to the workers who assign grades and/or cutting solutions through appropriate consoles.
Some automated grading systems have been proposed in the past, using complex image scanning and processing techniques applied on pieces of lumber travelling longitudinally over a conveyor. The prohibitive costs and the technical difficulties for implementing these systems have made them all but satisfactorily practical.
An object of the invention is to provide a lumber grading system which is simple in construction and operation, takes little space and adapts to existing sawmill equipment, can process a high volume of lumber, is inexpensive, reliable and efficient.
According to the present invention, there is provided a lumber grading system for providing a lumber cutting solution for a piece of lumber, comprising:
a first camera adapted to take an image of rear and bottom sides of the piece of lumber;
a second camera adapted to take an image of front and upper sides of the piece of lumber;
a first video acquisition means connected to the first camera, for acquiring the image generated by the first camera;
a second video acquisition means connected to the second camera, for acquiring the image generated by the second camera;
a computer means connected to the first and second acquisition means, for performing an image processing of the images and generating the lumber cutting solution for the piece of lumber based on preset grade determination parameters, the image processing including a longitudinal division of the images of the piece of lumber into a number of consecutive zones based on predetermined lumber cutting positions, an attribution of respective grades to the zones based on an image analysis of the zones as a function of the preset grade determination parameters, and a solution search providing the lumber cutting solution as a function of the grades attributed to the zones; and
a communication means connected to the computer means, for transmitting the lumber cutting solution.